Zn-ergic neurons are a subclass of glutamatergic neurons that are located in the cortical and limbic structures of the central nervous system. These presynaptic neurons accumulate vesicular zinc (Zn) that is released in a calcium and impulse-dependent manner. Zn released from these vesicles is thought to function as a neuromodulator in the adult brain by affecting receptors found at the surface of neurons. In addition to this potential role, Zn may also be important for early postnatal development of cerebral modules. The goal of this proposal is to clone a Zn transporter that is expressed in neurons that sequester Zn in synaptic vesicles. To assess the function of this transporter, the corresponding gene will be cloned and inactivated in embryonic stem cells by targeted gene disruption. These cells will be used to generate mice homozygous for the inactive allele and the effect on Zn accumulation within synaptic vesicles of Zn-ergic neurons will be assessed. If Zn sequestration is compromised, then this will provide an excellent system to assess the role of synaptic Zn in the development and function of the mammalian nervous system